1. Field of the Invention
The present invention relates to antenna modules including an antenna coil and a plurality of electronic components provided on a base.
2. Description of the Related Art
Conventionally, an antenna module of this type is used as, for example, a passive-type RFID (Radio Frequency Identification) tag. For example, as disclosed in Japanese Patent Laid-Open Publication No. 10-240889, it includes a card antenna (also known as “antenna coil”), a rectifier circuit, a regulator, an IC, and a base sheet on which these components are mounted.
The card antenna is a spiral-shaped antenna coil formed on the principal surface of the base sheet. This card antenna is electromagnetically coupled to an antenna of a reader/writer unit (hereinafter, “RWU”) which is provided outside the antenna module to produce an induced electromotive force. The rectifier circuit rectifies an AC voltage supplied from the card antenna and outputs a DC voltage to the regulator. The regulator converts the input DC voltage to a DC voltage which has a value suitable to driving of the IC, and supplies the resultant DC voltage to the IC. The IC is driven with the DC voltage supplied form the regulator.
In many of the antenna modules, the antenna coil used has a relatively large opening, and other electronic components are arranged in this opening portion. In this case, there is a probability that magnetic force lines generated from the antenna coil are blocked by the electronic components due to the arrangement of the electronic components. As a result, there is a problem that the characteristics of the antenna module (for example, directivity and communication distance) deteriorate.